已知:x+2y=1,x-2y=7,求x^2次方-4y^2的值.

已知：2x+y=6,x-3y=1 求7y(x-3y)(x-3y)-2(3y-x)(3y-x) 已知x+y=a,2x-y=-2a,求[（x/y-y/x)/(x+y)-x(1/x-1/y)]/[(x+1)/y]的值 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 已知x-y=1,求[(x+2y)^2+(2x+y)(x-4y)-3(x+y)(x-y)]除以y的值大神们帮帮忙 已知:【(x²+y²)-(x-y)²+2y(x-y)】/4y=1,求4x/4x²-y²-1/2x+y 已知x-y=1,求[(x+2y)²+(2x+y)(x-4y)-3(x+y)(x-y)]÷y的值 若x-y=2(x+y),求代数式x-y/x+y+x+y/x-y求代数式 x+y分之x-y+x-y分之x+y 已知:y=ax的3次方+bx+3,当x=-1/2时,y=-7,试求x=1/2时,y的值 已知|x|=2,|y|=3,|x+y|=-(x+y)求x-y 已知x-y=3,求[（x+y)(x-y)-(x-y)^2+2y(x-y)]除以的值 已知x≠y,x^2-x=y^2-y,求x+y的值. 已知3x =2y 求x/x+y+y/x-y-y²/x²-y² 1、已知x/y=7/2,求x/x+y 2、已知x/2=y/3=z/4,求x+y+z/2x+3y-z!1、已知x/y=7/2,求x/x+y2、已知x/2=y/3=z/4,求x+y+z/2x+3y-z! x+2y=2x+y+1=7x-y 求：2x-y? 把下列各式分解因式 x(x+y)(x-y)-x(y+x)² 2 已知2x+y=6,x-3y=1,求7y（x-3y）²把下列各式分解因式x(x+y)(x-y)-x(y+x)²7、已知2x+y=6,x-3y=1,求7y（x-3y）²-2（3y-x）³的值 已知x+2y=2x+y+1=7x-5,求x和y的值 已知x+2y=2x+y+1=7x-5,求x和y的值 已知：x,y满足|2x-y|+|y-1/2|=0,求7x-3y的值. 已知x、y满足2/1|x-y|+|1-y|=0,求7x-3y的值